1. Field of the Invention
This invention relates to a high-efficiency electric motor of electronic commutation type.
2. Discussion of the Background
High-efficiency electrical machines of electronic commutation type, hereinafter known as ECMs, operate with pulse modulation and generally at ultrasonic frequencies, with absorption of very high ripple current pulses. Without the use of a costly and bulky L-C filter in the feed line, the conducted and radiated electrical disturbance levels would be greater than allowed by current regulations. To reduce costs, the filter can be replaced by one of active type able to decouple the current absorbed by the electric motor from the battery current. A known and particularly effective implementation, in terms both of cost and performance, is to interpose between the battery and the ECM a step-up converter current-controlled by means of R.sub.FB on the basis of control information C.sub.FB originating from the ECM, which is compared with a velocity input V.sub.set by known methods. This converter is characterised by operating with an output voltage V.sub.c greater than the battery voltage V.sub.b and by absorbing from the battery an essentially continuous current (of constant delivered power) with a ripple as small as desired, achieved by dimensioning the inductor L and the switching frequency by known methods. The waveform of the battery current i.sub.b is shown in FIG. 2, which shows the typical times associated with the operation: 1/T is the switching frequency, T.sub.on and T.sub.off are the on and off times of the electronic power switch P (FIG. 1); also shown are the ripple superimposed on the mean absorbed current and the composition of i.sub.b, consisting of the sum of i.sub.P and i.sub.D, this latter being integrated by the capacitor C to provide a mean current i.sub.2 (from an essentially continuous V.sub.c) which powers the ECM.